All of this is pretty simple. Instacart simply needs to block ability of those that make an order from decreasing the tip after the order is live and automatica

All of this is pretty simple. Instacart simply needs to block ability of those that make an order from decreasing the tip after the order is live and automatically charge the shopper a penalty in the amount of the tip and service fee for accepting an order and not completing it. The first will remove incentives of customers to create orders that are tasty for shoppers under the false pretenses. The second one will make it costly for shoppers to accept good orders that they cannot complete.